The total mileage of railways in operation in China will reach 100 thousand kilometers by 2020, and “four vertical lines and four horizontal lines” of express dedicated passenger lines as well as three express intercity rail transportation systems will be constructed to achieve separation of passenger transportation and freight transportation practiced on busy main lines. Safe and comfortable running of dedicated passenger lines requires higher track regularity and stability, and brings profound technical renovation to track facilities in China.
At present, ballast tracks are generally applied to railways in China. The ballast beds of ballasted tracks gradually become loose due to being repeatedly passed by trains, thus resulting in poor irregularity and a great deal of maintenance work. In addition, the development of increasing the speed of railway is hindered by the workload and time required by maintenance.
France, which is a country with high-speed railways with ballasted tracks as the representative, has always been proud of the ballasted tracks operating at 270 km/h to 300 km/h. However, it's found later that railway ballast of the southeast line and Atlantic line early established is pulverized seriously. The geometric dimensions of the tracks are hardly maintained. Maintenance periods are shortened, maintenance costs are largely increased, and even normal operation is affected. Complete overhaul has to be performed and the railway ballast has to be replaced until it is even operated for less than a decade.
Ballast-less track technology has been developed maturely in the countries mainly comprising Germany and Japan. The slab-type tracks in Japan have relatively unified constructions which however have structures and dimensions slightly different for different line grades, different natural conditions, different basic conditions, and different train speeds and operating conditions. The slab-type tracks are classified into certain types which currently include a common A type, a frame type and a practical vibration reduction G type applied in special vibration reduction sections etc.
Ballast-less tracks have been researched in China since the 1960s which was as early as abroad. Supporting block-type integrated ballast beds, short wooden sleeper-type integrated ballast beds, and integrally cast integrated ballast beds etc., frame type asphalt ballast beds and the beds of many other types were applied in trial laying at the preliminary stage. Supporting block-type ballast-less tracks which are about 300 km long used to be laid in tunnels of the Chengdu-Kunming Line, the Beijing-Yuanping Line, the Beijing-Tongliao Line and the Southern Xinjiang Line. Afterwards, asphalt concrete ballast-less tracks consisting of asphalt concrete pavement layers and wide sleepers were applied in trial laying only in large-scale passenger railway stations and tunnels. Ballast-less structures without sleepers also used to be laid on the Jiujiang Yangtze River Bridge of the Beijing-Kowloon Line. Currently, high-speed railways, dedicated passenger lines, as well as urban and intercity transportation in China are constructed step by step. Since trains are operating at higher speed with less maintenance time, adequate consideration should be taken to achieve comfortable, stable, and durable ballast-less tracks with less maintenance.
Ballast-less track systems are applied to most high-speed railways all over the world, and there are two major types of ballast-less tracks, i.e. slab-type ballast-less tracks and double-block type ballast-less tracks. Compared with ballast-less tracks of the double-block type, slab-type ballast-less tracks with post-tensioned track slabs in Japan and Bögl slabs in Germany as the representative are evidently advantageous.
High speed railway ballast-less tracks have been developed rapidly since post-tensioned track slabs were applied to the Qinhuangdao-Shenyang Line and the Suining-Chongqing Line on trial and then Bögl slabs were applied to the Beijing-Tianjing intercity high-speed railway. It's proven by engineering practice that these two kinds of track slabs have evident disadvantages and need to be improved.